MySQL Forums :: Newbie :: Time syntax question for calculating a set of values

SELECT  DATE_FORMAT(PaymentDate, '2012-%-%') AS "Month",
        AVG(PaymentAmt) AS "Average Payment"
    FROM  Payments
    WHERE  PaymentDate BETWEEN '2012-09-01'  AND  '2012-09-30'
      AND  PaymentDate BETWEEN '2012-07-01'  AND  '2012-07-31';

You want rows that are simultaneously in September and in July?
Perhaps you meant OR instead of AND. (The English language is tricky.)

Reade DATE_FORMAT again...

mysql> SELECT DATE_FORMAT(NOW(), '2012-%-%');
+--------------------------------+
| DATE_FORMAT(NOW(), '2012-%-%') |
+--------------------------------+
| 2012--%                        |
+--------------------------------+


mysql> SELECT DATE_FORMAT(NOW(), '2012-%m-%d'), NOW();
+----------------------------------+---------------------+
| DATE_FORMAT(NOW(), '2012-%m-%d') | NOW()               |
+----------------------------------+---------------------+
| 2012-04-09                       | 2012-04-09 05:44:22 |
+----------------------------------+---------------------+